Bleach has three flaws:
First, it's popular and a lot of the fanbase are little kids, so you can't talk about it online without running into waves of idiots and trolls. This isn't technically a flaw with the series itself, but since a lot of the enjoyment for anime/manga comes from discussing them with other people, it does effect how fun the series is to read.
Second, like all weekly manga, all popular manga, and especially all shonen jump manga, it has horrendously slow pacing. Way to milk your plotline for all it's worth, editors.
Third, the thing is so fucking long and has so many cast members that you need god's own memory to keep track of the characters.
Other than that, it's a good series. Nothing original, to be sure, but it's one of the better iterations of the fighting shonen formula, and certainly the best thing the Jump's running these days now that they canceled Mx0.